GOST 26007-83

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  ГОСТ 26007-83

GOST 26007−83 Calculations and strength tests. Methods of mechanical testing of metals. Test methods for stress relaxation

GOST 26007−83

Group B09

STATE STANDARD OF THE USSR

Calculations and strength tests.
Methods of mechanical testing of metals

TEST METHODS FOR STRESS RELAXATION

Design, calculation and strenght testing.
Methods of mechanical testing of metals. Methods for stress relaxation testing.

AXTU 4109

The introduction from 01.01.85
to 01.01.90*
______________________________
* Expiration removed
Protocol N 4−93 Mezhgosudarstvennogo Council
for standardization, Metrology and sertifikatsiia
(IUS N 4, 1994). — Note the manufacturer’s database.

DEVELOPED

The Ministry of power engineering

USSR state Committee on standards

PERFORMERS

A. A. Chizhik, d-R tekhn. Sciences; 3.M. Peter and Paul, d-R tekhn. Sciences; V. D. Tokarev, candidate. tech. D. (leader); A. A. Lanin; G. G. Morozov, Cand. tech. Sciences; E. I. TAVER, PhD. tech. Sciences; T. N. Samoilova, O. N. Andreev, V. A. Metel’kov, candidate. tech. Sciences

INTRODUCED by the Ministry of power engineering

Head of Technical Department V. P. Goloviznin

APPROVED AND put INTO EFFECT by Decision of the USSR State Committee on standards of 15 December 1983, N 5972

This standard specifies test methods for stress relaxation at temperatures up to 1200 °C tensile, bending and torsion of ferrous and nonferrous metals and alloys.

The essence of the methods consists in that the test sample is determined by the change in voltage in time at constant total strain calculation of the sample equal to the predetermined initial deformation.

This standard does not apply to structural elements of machines, devices and apparatus.

1. GENERAL PROVISIONS

1.1. Conventions used in the standard given in the informational Appendix 1.

1.2. Test methods are divided into direct and indirect.

Direct methods include tests at constant total strain.

Indirect methods include tests at constant total displacement.

1.3. The kinds of loading test methods are divided into test under uniaxial tension, bending, shear and torsion.

1.4. On the accuracy of determining the variation of stresses in time, all the estimation methods of stress relaxation are divided into three categories.

The first category includes methods to ensure the accuracy of determining the voltage not more than 5% of the measured value at any moment of the test.

The second category includes methods to ensure the accuracy of the determination voltages is not more than 15% of the measured value at any moment of the test.

The third category includes methods to ensure the accuracy of the determination voltages not exceeding 25% of the measured value at any moment of the test.

1.5. The requirements for testing, all methods are divided into two groups:

the first group — without razgryzaniya in the mode of automatic maintenance of the constancy of the total deformation in the test process;

the second group of tests with periodic unloading.

The first group is used for testing all categories of accuracy.

The second group is used for testing the second and third categories of accuracy.

1.6. Allowed estimation of stress relaxation of materials according to direct tests of creep under uniaxial tension in accordance with the requirements of GOST 3248−81. The accuracy of the estimates should not be lower accuracy categories stipulated in clause 1.4.

1.7. The accuracy category and test group must be specified in the standards and technical conditions for steel products, which establishes technical requirements for it.

2. SAMPLES

2.1. Depending on the accuracy categories used samples of different sizes, given in PP. 2.1.1−2.1.3.

2.1.1. For all categories of precision tensile:

cylindrical with a diameter of 10 mm working length 100 and 150 mm;

flat width 10 mm working length 100 mm, sample thickness is determined by the thickness of the sheet;

other dimensions working length where the cross — sectional area of specimen before test, mm.

The diameter of the cylindrical specimen should not be less than 5 mm.

Thickness of flat specimens shall be not less than 3 mm.

Sample sizes given in the recommended Appendix 2.

2.1.2. For the second category of accuracy — sample of equal resistance to bending dimensions of hell. 1 mandatory Annex 3.

2.1.3. For the third category of accuracy:

sample tensile working length ,

a sample of equal-sized section with sizes of features. 2 required applications 3;

the spring sample with a square cross work turns to shit. 3 3 required applications.

The ratio of the average diameter to the width of the cross section of the coil should be not less than 3, the number of turns is at least 2, the height of the cylindrical part at least .

2.2. Permissible deviations on dimensions and the surface shall conform to the requirements of table. 1.

Table 1

2.2.1. The allowable deviation from the calculated length of sample (length of sample area, which is set constant in time move) for all categories of precision:

for tensile specimens — no more than ±0.5% of calculated length;

for samples of equal resistance to bending — not more than ±0,5% of the inner diameter;

for samples equal-section — no more than ±0.5% of specified average diameter;

for spring samples — less than ±0,5% of the average diameter to the number of turns.

2.2.2. The allowable deviation value of the cross-sectional area in all cross-sections calculated:

for all categories of precision cylindrical samples under tension of ±0,5%;

for the first category of accuracy — flat samples in tension ±1%;

for the second category of precision — flat samples in tension ± 1,5%;

samples of equal resistance to bending ±3%;

for the third category of the precision — flat samples in tension ±2%;

samples of equal resistance to bending ±4%;

samples of equal cross-section ±3%;

spring samples ±5%.

2.2.3. For all categories of precision radial runout of the specimen in tension shall not exceed 20 microns. The deviation from flatness for flat specimens, machined from all sides at the 15th degree of accuracy GOST 24643−81.

For the third category of the precision radial runout spring sample should not exceed 0.005 times the value of the average diameter.

The assembled LRO of the spring sample should not exceed 0.005 times the value of the average diameter.

2.3. The shape and dimensions of the heads of the tensile specimens determined by the method of mounting the meter on the sample and method of fixing the specimen in the grips of the testing machine.

The mate of the head of the sample with its design part should be smooth. The head diameter of the sample should be not less than two diameters of the working part.

2.4. When testing samples of heat-treated, the heat treatment must be blank for samples.

Requirements for metal and size of the workpieces and their clippings are established by standards or specifications for steel.

2.5. Samples with warpage, mechanical damage, surface defects such as foreign inclusions, delaminations, pores, cavities, cracks (caused by heat treatment) to tests are not allowed.

2.6. On samples of equal resistance to bending and spring samples must be applied to the prints used for reference strain measurements during the test.

The prints shall be marked where indicated on the devil. 1−3 required applications 3.

For the application of the prints is recommended to use standard tools for measuring the hardness according to GOST 2999−75.

During long trials, if as a result of oxidation of the clarity of the prints is lost, apply new prints.

Prints allowed to put on the plates of heat-resistant materials, pre-napisannyj on the sample.

2.7. Marking of cylindrical and flat specimens in tension need to produce at the ends of the heads and samples of equal resistance to bending and spring samples at the locations specified on the devil. 1−3 required applications 3.

2.8. In the selection of a party samples for testing the stress relaxation in terms of hardness, the hardness measurement carried out in accordance with GOST 9012−59 elegost 9013−59.

2.9. In the manufacture of samples should not be a change of structure and properties of the tested metal.

Allowed the samples to expose the release to relieve residual stresses.

3. EQUIPMENT

3.1. For testing requires the use of testing machines and devices that meet the requirements of this standard.

3.2. The energizers devices machines and appliances for testing metals for the stress relaxation shall not show deviations greater than ±0.5% of actual load, and must also ensure the maintenance of a constant total strain on the calculated part of the specimen throughout the testing process, with the deviation of the displacement should not be more than:

±0,003 mm for tensile specimens;

±0.010 mm for samples of equal resistance to bending;

± 0.050 mm, for spring samples.

3.3. The heating device must provide uniform heating of the samples throughout the calculated length to a predetermined temperature and maintaining the latter during the entire test.

For cylindrical and flat specimens in tension deviations from the specified test temperature at any point of testing time and at any point the calculated length of the sample must not exceed:

±3°C — 600 °C;

±4°C from 600 to 900 °C;

±6°C from 900 to 1200 °C.

For samples of equal resistance to bending and spring samples is not more than ±6°C at the heating temperature to 1200 °C.

3.4. On cylindrical and flat specimens in tension should be set at least three thermocouples evenly throughout its length.

The samples for bending and spring samples shall be equipped with one thermocouple anywhere on the calculated of the sample.

4. TESTING

4.1. For all kinds of loading during the test is set to the constant move :

for a cylindrical sample — elongation in the direction of application of a tensile load along the axis of the sample;

for samples in bending — the opening of the slot in the plane of the sample;

for spring samples, shortening along the axis of the sample.

While for cylindrical samples under tension and spring samples is performed the condition of a constant total strain (direct methods) for circular — the only move (indirect methods).

4.2. Testing at a given temperature is carried out on at least three levels of primary voltage, at each level of experience at least two samples.

4.3. Elastic displacements ( — start and  — after time from beginning of test) are determined as the difference of the measurements of the displacements for the loaded condition and unloaded .

4.4. The order of testing samples in the mode of automatic maintenance of the constancy of the strain following.

Mounted in the grips of the testing machine and placed in the oven the sample was heated to test temperature and maintain it at this temperature until complete warm-up for at least 2 h and Then loaded onto the sample and simultaneously include a system to automatically maintain a constant deformation on the calculated part of the sample, in this case, record the load change continuously or with an interval in order to establish the nature of relaxation.

The rate of rise of tension in the specimen during loading should not exceed 700 MPa/min.

When loading to a given deformation is not allowed the elongation of the specimen due to creep more than 0.01 mm due to non-synchronization switching on the system automatically maintain the deformation and loading of the sample.

4.5. The order of testing the samples at periodic unloading next.

The sample is loaded at a temperature of (20±5)°C at design load, while the fixed displacement should be .

Determine the displacement .

Measure the distance between prints. Then the sample is loaded up to the rated voltage at a temperature of (20±5)°C and measure the distance between prints.

In the loaded state, the sample is placed in a chamber of the heating device. After the time the sample is removed from the oven, cooled in a loaded condition to a temperature of (20±5)°C, measured  — the distance between the prints, followed by unloading and measuring the distance between prints.

After that, expect elastic displacement , which is stored in the magazine tests. Then the sample is again loaded up and after checking with a deviation of ±0.01 mm is placed in a chamber of the heating device.

Note. It is recommended that periodic unloading is done using 0.1% of set time tests, unless you want another time of discharge.

4.5.1. For fixing the movement of specimens tested in bending, it is allowed to use the wedges (see the devil. 1 mandatory Annex 3), the test samples-spring — bushings (see the devil. 4 mandatory Annex 3). The materials of the wedges and bushings should be selected with coefficients of linear expansion close to linear expansion coefficient of the sample material, and differing from it no more than 5% for the second category of precision and 10% for the third category.

4.5.2. The thickness of the wedge, mm, when the bend test is determined by the formula ; the height of the sleeve , mm, when tested the spring of the samples is determined by the formula .

4.5.3. When you insert the wedge in the sample in bending overload of the sample should not exceed 5% of the values of the design stresses.

4.6. The distance between the prints , and should be measured on a tool microscope with a scale division of not more than 0.005 mm. the room Temperature during the measurement shall be (20±5) °C.

4.7. Constant during the test displacement shall be determined by the formulas:

for cylindrical or flat specimen tensile

;

for a sample of equal resistance to bending

,

where =0,000583, 1/mm;

for sample bending equal sections

,

where =0,000702, 1/mm;

for spring sample

where ;

 — coefficient table. 2;

Table 2

for spring sample in terms of tensile

where ;

 — coefficient table. 2.

4.8. The magnitude of the calculated stress shall not exceed:

.

5. PROCESSING OF THE RESULTS

5.1. Processing of the results consists in determination of elastic stresses in the sample during the test.

5.1.1. When testing without discharge:

tensile by dividing the load on the cross-sectional area calculation of the sample measured prior to testing;

bending and torsion — dividing the magnitude of the bending moment to resistance moment calculation of the sample measured prior to testing.

5.1.2. When testing with periodic unloading of the sample is carried out according to the formulas:

or .

5.2. Relaxation curves are built in coordinates: «the ordinate is the voltage in a uniform scale, the abscissa is the time in logarithmic scale». Extrapolation of the results is carried out graphically by linear continuation of the curve in the specified coordinate system, but not more than one order at a time.

Note. Allowed to use other coordinates for the curves of relaxation. In this case, the test protocols, reports and technical documentation when placing the interpolated and extrapolated values of voltage indicates the selected coordinate system.

5.3. Test results on stress relaxation for each sample is recommended to record in the minutes in the form given in recommended Appendix 4.

5.4. When the results of the tests indicate: the type of loading (tension, bending, torsion), type of sample, number of samples for each value of the initial voltage, a method of processing results (graphical and statistical), the maximum duration of the tests and extrapolation of test results.

ANNEX 1 (reference). CONVENTIONS USED IN THE STANDARD

ANNEX 1
Reference

When tested for stress relaxation are accepted designations:

gauge length of the specimen , mm — section of the sample on which to maintain the constancy of the total displacement;

the working length of the sample , mm — section of the sample, the creep deformation which leads to stress relaxation;

the initial diameter of the working part of the cylindrical sample in tension , mm;

the initial thickness of the working part of a flat sample , mm;

the initial width of the working part of a flat sample , mm;

the initial slot width of the annular specimen , mm;

the initial thickness of the coil spring of the specimen , mm;

the linear dimension of the locking movement , mm. For ring specimens -the width of the wedge for spring samples — the height of the sleeve;

the outer diameter of the spring sample , mm;

the average diameter of the spring sample , mm;

the number of working turns of the spring sample ;

the height of the spring sample , mm;

the height of the cylindrical part of the spring sample , mm;

the initial cross-sectional area of the working part of the sample , mm, in the case of samples of equal cross-section;

the initial distance between the control prints the hardness of the samples without load , mm, at normal temperature (20) °C;

the distance between the control prints the hardness of samples after load, mm, at normal temperature (20)°C;

the distance between repernye prints the hardness of the samples after unloading through time , mm, at normal temperature (20)°C;

a predetermined constant during the test, displacement of the specimen , mm (normal temperature , mm);

residual elastic displacement of the sample, determined after unloading using the time , mm (normal temperature from the ratio );

the normal elasticity modulus at test temperature , MPa (kgf/mm) (at normal temperature , MPa (kgf/mm));

the shear modulus at test temperature , MPa (kgf/mm) (at normal temperature , MPa (kgf/mm));

the initial normal and shear stress, MPa (kgs/mm);

the residual normal and shear stress, MPa (kgs/mm);

the yield strength at test temperature , determined according to GOST 1497−73.

APPENDIX 2 (recommended). SAMPLES FOR TESTING

ANNEX 2
Recommended

Damn.1. The cylindrical sample

The cylindrical sample

Damn.1

mm

Damn.2

Damn.2

Damn.3. Sample flat

Sample flat

Damn.3

APPENDIX 3 (obligatory). SAMPLES FOR TESTING

APPENDIX 3
Mandatory

Damn.1. A sample of equal resistance to bending

A sample of equal resistance to bending

Damn.1

Damn.2. Sample equal sections

Sample equal sections

Damn.2

Damn.3. Spring sample

Spring sample

Damn.3

Damn.4. Spring sample with sleeve

Spring sample with sleeve

Damn.4

APPENDIX 4 (recommended). PROTOCOL TESTING OF METALS FOR THE STRESS RELAXATION

ANNEX 4
Recommended

1. MATERIAL

1.1. Name brand (to the appropriate standard).

1.2. Chemical composition.

1.3. Smelting (furnace type) and size of ingot, billet.

1.4. Kind of steel (rolled section, casting).

1.5. The types and modes of heat treatment.

1.6. Mechanical properties (; ; ; ; ) at 20 °C and the test temperature and hardness at 20 °C.

1.7. The normal elasticity modulus at the test temperature.

2. SAMPLES

2.1. The place from which sample taken.

2.2. Type and size of sample.

3. EQUIPMENT

3.1. Installation type for the test.

3.2. The accuracy of temperature measurement.

4. THE CONDITIONS AND TEST RESULTS

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M.: Publishing house of standards, 1984